1. Technical Field
This disclosure relates to an image forming apparatus, and more specifically to an image forming apparatus including one or more recording heads for ejecting droplets.
2. Description of the Related Art
Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional devices having two or more of the foregoing capabilities. As one type of image forming apparatus employing a liquid-ejection recording method, inkjet recording apparatuses are known that use one or more recording heads (liquid ejection head or droplet ejection head) for ejecting droplets of ink or other liquid.
Such a liquid-ejection type image forming apparatus may have a head tank (also referred to as sub tank or buffer tank) to supply liquid to a recording head and a liquid supply system to supply liquid to the head tank via a supply tube (supply passage) from a main tank (ink cartridge) removably (replaceably) mounted on an apparatus body.
For such a liquid supply system, if the liquid feed pump continues to be driven to feed liquid with the ink cartridge empty, the internal pressure of the ink cartridge and the supply passage becomes a negative pressure. When the ink cartridge is removed from the apparatus body for replacement, air intrudes into the supply passage. Such air is delivered as bubbles from the head tank to the recording head, thus causing ejection failure.
Hence, for example, an inkjet recording apparatus may have a reversible pump as the liquid feed pump. If the liquid feed pump feeds ink from the main tank to the head tank with the main tank being short of ink, the liquid feed pump feeds ink in reverse from the head tank to the main tank to prevent air from intruding into the supply passage (see JP-2011-051294-A and JP-2010-155446-A).
However, if the liquid feed pump is driven for reverse rotation to feed ink in reverse with the remaining amount of ink in the head tank being small, air may be inhaled into the supply passage. Hence, JP-2011-051294-A proposes an inkjet recording apparatus having a liquid level detection member to detect the height of the liquid level of ink in the head tank. Even in a case in which the liquid feed pump feeds ink from the main tank to the head tank with the main tank being short of ink, when the height of the liquid level of ink in the head tank is a threshold height or lower, in other words, the liquid level detection member does not the liquid level, the liquid feed pump does not perform reverse rotation feeding to prevent air from being inhaled from the head tank into the supply passage connected to the main tank.
However, the inventor has recognized that, for a configuration in which a supply port member of the supply passage is located at a position lower than the liquid level detection member in the head tank, if the liquid feed pump is controlled so as not to feed ink in reverse when the liquid level detector does not detect the liquid level as described in JP-2011-051294-A, a situation occurs in which the liquid feed pump does not feed ink in reverse in spite of being able to feed ink in reverse, thus resulting in an increased risk of air bubble intrusion on replacement of the main tank.